


Lab Rat

by mumsywrites



Category: Fire Emblem: Fuukasetsugetsu | Fire Emblem: Three Houses
Genre: For Science!, M/M, Masturbation, NSFW, Post-Time Skip, Post-Timeskip | War Phase (Fire Emblem: Three Houses), Simple as that, Witty Banter, and sex, but I don't get into it, linhardt wants to study sylvain's crest, most likely azure moon route
Language: English
Status: Completed
Published: 2020-05-23
Updated: 2020-05-23
Packaged: 2021-03-03 01:35:16
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,237
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/24342877
Author URL: https://archiveofourown.org/users/mumsywrites/pseuds/mumsywrites
Summary: Linhardt is curious about the nature of Sylvain's crest. Could his loose and reckless behavior be a result of his crest's abilities? There's only one way to find out...
Relationships: Sylvain Jose Gautier/Linhardt von Hevring
Kudos: 54





	Lab Rat

**Author's Note:**

> All it takes is a cute fanart on twitter and BAM, I'm shipping a rare-pair and writing a fic. Just wanted to have fun. Enjoy!

Linhardt woke up to the usual fogginess he welcomed after a good night’s sleep. The noon-day light was creeping in at just the right angle to help flutter his eyes open. What wasn’t normal was the soreness in his lower back; that was new. He turned about in the bed and spotted Sylvain, fully dressed and sitting at his desk.

He turned and shot Linhardt a smile that had definitely been used and rehearsed thousands of times before. “Well, look who decided to wake up.”

Linhardt would have rolled his eyes if he had the energy to, but yawning would have to suffice for the time being.

“It’s not normal for me _not_ to wake up next to my nightly guest, but dude. It’s so late.”

“There’s nothing against you sleeping in, is there?” Linhardt curled up in the sheets, taking a deep breath as he buried his face into the warm fabric. Sylvain left an interesting musk behind; Linhardt was sure to make note of that in his research later.

“Enjoying yourself?”

“More than you seem to be, it seems,” Linhardt said, noticing the tone in Sylvain’s voice had grown a little more irate.

“Yeah, well, I couldn’t really skip on the war council meeting. And Felix would have kicked my ass if I even joked about skipping his morning training session.”

“What a dull morning. Sounds like you should have slept in.”

“With you?”

Lindhardt stretched his arms out, letting his back curve and give out a nice crack. The bedsheets slid down his chest, revealing every bite and hickey Sylvain had made the night before. “You weren’t opposed to the idea last night.”

“Apparently not,” Sylvain said, leaning forward in his chair to get a closer look. “I did quite the number on you, didn’t I?”

“I’d say,” Linhardt said, sitting up and rubbing at his lower back.

“Well,” Sylvain started, a smirk growing across his lips, “you did mention I was your first.”

Linhardt breathed in deeply through gritted teeth, trying to suppress any flush from appearing on his cheeks; it was a tried and true method he had perfected since childhood. “Which should have prompted you to take it easy, one might imagine. But apparently you didn’t seem to grasp that concept, did you? I guess I’ll make a note of that in my research as well.”

Sylvain rolled his eyes. “I don’t understand how this is going to help you with your crest research,” he said, grabbing Linhardt’s tunic from the ground and tossing it towards the bed. “In order to find a consistent trend, you’d have to sleep with my dad, too.”

Linhardt shrugged and pulled the tunic over his head. “Well, if the Kingdom ends up winning this war, it’ll be much easier to ask if he’d be interested.”

“Goddess, you’re serious…”

Linhardt threw the bedsheets from his body and swung his legs over the edge. Unfortunately, standing had become a much more daunting task after the evening’s activities. His knees buckled beneath him and he began to collapse to the floor, but Sylvain was able to catch him quickly in his arms.

“Easy, there,” Sylvain said, his hand cupping gently at the crook in Linhardt’sback. “Especially for a first timer, the first step in the morning is always the hardest.”

Lindhardt found himself completely off guard and allowed the flush to fill his cheeks without bothering the tame them back. It was just…really nice being held by Sylvain. Quite frankly, he enjoyed it. He enjoyed his strong arms, built up with muscle after years of warfare. Hands, gentle yet deliberate from years of chasing skirts and entertaining bed partner after bed partner. Perhaps these were independent variables to take into consideration.

Sylvain leaned in close, brushing his nose up against Linhardt’s. “Care for another round before lunch?”

Linhardt winced at the throb in his backside. “You know, I’d much rather return to my room and get my notes sorted out before we meet like this again.”

Sylvain laugh and released Linhardt from his hold. “Notes? You took notes last night?”

“Of course,” Linhardt said, steadying himself as he managed to collect the remainder of his clothing from about the room. “All in my head, of course. I need to write them all down and get them organized. The quicker I do, the better.”

“Fine, I’ll eat lunch alone.”

Laughing, Linhardt pulled on his pants and rolled his eyes at Sylvain. “I hardly think that will be the case. I often see you with a dining partner. Odds are, you’ll find one.”

“Thanks?”

With a shrug, Linhardt was out the door and into the hallway.

“So. You mentioned you wanna do this again,” Sylvain said, leaning up against the door frame. Linhardt could almost see the wear in the wood from the amount of times he made that pose. “I’d be down…”

“Of course, though I’d rather not come up to your room again. It’s such a bother going down this long hallway.”

“So…your room?”

Linhardt gave the proposition a thought before giving a quick nod. “Yes. That would be best.”

“Then I’ll see you tonight,” he said the to sound of his doors shutting.

Linhardt sighed. “He’s a curious one…”

* * *

Linhardt spent several hours recounting his memories from the previous night to write his notes down on paper. He normally took pride in his impeccable memory, but for the moment, it seemed to be causing some new, unexpected problems. He had to start from the beginning of the evening, after he approached Sylvain for potential crest research.

“Welcome,” Sylvain had said, opening the doors to his oddly clean room.

“Interesting,” Linhardt responded. “I didn’t take you as the type to be so clean and orderly.”

“How do you expect me to entertain my guests if my room is a sty? Come on, Linhardt, I’d expect you to understand at least that much.”

Linhardt jotted down:

_Room regularly cleaned and dusted to impress potential sexual partners._

He glanced around his own room and noticed the piles of books and scattered papers lying about. “Hm,” he said, the feathers of his quill pen brushing against his face. “Perhaps I should tidy a bit before he comes over.” He thought it through for a moment before shrugging off the idea as too bothersome. He only had one note down and distractions would not be tolerated.

“So, how do your evenings generally start?” Linhardt had asked Sylvain the night before.

Sylvain hadn’t answered with words, rather with his body. His hand had rested on the back of Linhardt’s neck while the other took him by the waist to pull him in close for a kiss.

The hairs at the back of Linhardt’s neck raised at the memory. Calloused as Sylvain’s hands normally were, they were strangely soft the previous night. And his touch…his hold was so gentle it was almost as if he weren’t touching Linhardt at all, but he exuded a type of control that Linhardt wouldn’t have been able to break free from his arms. The memory nearly took the breath from Linhardt’s lungs and he sat with his quill, unmoving. How could he write that part of the encounter down in words?

 _Ability to embrace partners with extreme control and precision_ , he eventually scribbled out. But he wasn’t happy with that. No, too subjective. He groaned and leaned back, staring towards the ceiling. “This is quite difficult.”

But the kiss…

Linhardt closed his eyes to remember. Just lips touching at first, but Sylvain had coaxed Linhardt’s mouth to open. He couldn’t remember how, but moments after, Sylvain’s tongue had found its way in his mouth. He tasted…

A pulse in Linhardt’s groin began to throb softly. He opened his eyes and sat up. “Come on, Linhardt. Stick to the research.”

 _Body language strong enough to affect partner’s choices_. He rolled his eyes. “That’s terrible.”

The kiss had lead to Linhardt’s clothing on the floor. He couldn’t remember exactly how they came off, in what order, or how he ended up on the bed, legs wrapped around Sylvain’s still clothed body. That did not bode well for his notes; breaks in his memory were rare. “Perhaps I should have taken notes during our…session…”

…legs wrapped around Sylvain; Sylvain’s hands running down from his waist to his hips to his thighs. The throbbing returned, and this time Linhardt couldn’t ignore it. The memory from the previous night had caused an erection to form. He whined, looking down at his pants with disappointment. “Well, this isn’t good.”

_Subject able to control partner’s libido telepathically._

…down his thighs, between his thighs, cupping his ass…

The temperature in the room had risen, or so he thought. Why else would he be sweating? His hand was shaking and quill, pressed down on the paper, began scribbling nonsense upon the note-sheet. “Dammit,” he spat, placing it down and staring at the main distraction between his legs. “Curse that Gautier.”

He slipped a hand into his pants and wrapped it around his erection, his thumb nearly hovering over the tip. The sooner he took care of this distraction, the sooner he could return to his notes.

…Sylvain had taken off his shirt, revealing a body more built that even Caspar’s and littered with more scars than Linhardt was prepared to see. He tossed it aside and looked down at Linhardt, giving him a smirk and a wink…

“A-ah,” Linhardt cried as he pressed his thumb down, swirling it about the tip, his other fingers shaking as they glided up and down. He wasn’t expecting this sort of reaction to recounting his memories, but Sylvain was apparently a master of seduction, both in person and in memory. Just the thought of how he had bit and nibbled at the flesh on his neck, on his chest, his hands roaming and probing.

“S-sylvain,” he called out without thought, his grasp tightening and his rhythm steadily increasing.

“You called?”

He nearly came at that moment, due to shock rather than pleasure. He turned, Sylvain seeming to materialize from Linhardt’s mind, leaning against the door frame in that signature pose.

“You could have knocked,” he said, his hand still firmly handling his own cock.

Sylvain laughed and stepped inside, closing the doors behind him. “I did, but you didn’t answer. And then I heard, well…”

“I _was_ trying to get my notes down, but…”

“But the thought of me was too irresistible, right?” Sylvain put a hand on Linhardt’s shoulder which only worsened his current predicament. He craned his neck to read the notes.

“Control my partner’s libido telepathically? I wish. You know how cool it would be to have a power like that?”

“Well, apparently you do! Look at…”

“This isn’t me controlling you. This is just you getting hot thinking of me. This is a you problem, Linhardt. Not a result of my crest’s abilities.”

Again, Linhardt was struggling to find the right words, but it didn’t matter as Sylvain’s hand joined his around his cock, those surprisingly smooth hands. Just the feel of them on his body, lacing between his fingers and guiding his hand along his length. Linhardt’s shoulders rolled back as the sensation ran up his spine. His head bent over the top of his chair and Sylvain caught his mouth in another kiss.

That taste again, and his scent. Linhardt couldn’t put it in words, but he wished to be enveloped in it. He reached up with his free hand, running his fingers through red tresses, finding a long scar long hidden beneath. He ran his finger along it and Sylvain laughed his way out of his mouth.

“Are you enjoying this?”

He looked up into those amber eyes and swallowed hard. “We should…continue our research.”

Laughing, Sylvain glanced back at the bed. “Yeah, well, your room is a mess…”

Linhardt struggled to get up from his seat, but managed to hobble over to the bed and tossed aside all the books and papers that had been there. “We can…make do…”

“If you insist,” Sylvain said with a sigh as he removed his shirt.

Linhardt stared, trying to resume his mental notes; scars on almost every inch of skin. Some were freshly healed, some were old and white, the skin seeming to have stretched with Sylvain as he grew older over the years. He found those most interesting.

Sylvain advanced on Linhardt, their mouths meeting once more and Sylvain’s hand returning to its place in Linhardt’s pants.

Linhardt fell back, fingers locked behind Sylvain’s neck, and brought him down with him. That taste again, almost sweet. His tongue couldn’t get enough, pushing past Sylvain’s lips to consume what he could. His whole body quivered, more beads of sweat staining his clothes, his accursed clothes that somehow were still on…

Sylvain’s free hand was able to solve that problem and swiftly removed Linhardt’s tunic, breaking from the kiss only for a moment to pull it over his head.

Linhardt’s hands gripped at the back of Sylvain’s shoulders. His fingers explored the grooves of his muscles, clinging to whatever he could.

Sylvain’s free hand now worked to remove Linhardt’s pants, his busy one increasing a rhythm as Linhardt was reaching his limit.

With a bite to the lower lip, Sylvain pulled back and smirked down. “Are you certain this is all for research? Are you positive you’re just not horny for me?”

What was he even saying? Why did he stop kissing him? Why did his hand stop moving? Linhardt groaned and he slipped his hands into the back of Sylvain’s pants, tightly grasping his ass. “I don’t recall telling you to stop.”

Sylvain laughed, shaking his head. “You’re a funny one, Hevring.” He reached into his pocket and produced a crystal vial, the same one from the previous night.

Of course! How could Linhardt forget? He needed to know the exact contents of the vile. “What…what is that?”

“I makes everything run a bit smoother,” Sylvain said, popping off the stopper and pouring a decent amount on his fingers. “Remember? Last night?”

“That’s…” Linhardt was becoming annoyed, and uncomfortable. His erection was in dire need of attention at this very moment. “I mean the ingredients! What’s in that vial? How does it…”

“You know,” Sylvain said, studying the viscous liquid as it coated his fingers. “That’ll spoil the fun. And to be frank, has nothing to do with my crest, so let’s just…”

He didn’t see Sylvain’s hand move, but it slipped up between Linhardt’s legs and towards his ass. Two fingers pushed in, the chill of the liquid sending a jolt up Linhardt’s spine. His back arched, allowing Sylvain to probe deeper.

“…let’s just continue having fun.”

Linhardt’s hands flew back to the sides of his pillow, gripping it tightly as Sylvain’s fingers moved inside, spreading him open, prepping for the eventual penetration. Why did he have to wait? Why couldn’t he just do it now? Linhardt couldn’t make sense of his thoughts, but he desperately wanted Sylvain inside of him. The wait was pure hell.

Sylvain’s fingers slipped out, moving to lift Linhardt’s legs, resting one of them on his shoulder. “I’d ask if you were ready, but…I can tell.”

Linhardt swallowed hard and looked up, giving Sylvain a desperate nod.

“Good.”

In seconds, the tip of Sylvain’s cock was pressed up against Linhardt’s ass, and with a little bit of extra probing, he was inside. His body twitched and his head rolled about his pillow as Sylvain pushed in deeper. With one hand gripped on his ankle, the other, still covered in the contents of the vial, firm on his hips, Sylvain began to move, slowing rocking in and out.

Linhardt looked up, trying to focus on Sylvain’s face. His eyes were closed, his brow tightly creased, his jaw slightly agape. His hair was matted to the sweat on his forehead, while the tresses further back swayed with his thrusts. Linhardt moaned and tossed his head back again. Every thrust hit him deep and the throbbing of his own cock returned. He reached down with a shaky hand, only to be met by Sylvain’s once more. He looked up again, those amber eyes narrowed, a sly smirk greeting him.

With a nod, Sylvain’s hand guided Linhardt’s up and down, to the rhythm of his own thrusting.

Linhardt nearly cried out, but Sylvain leaned it, letting go of Linhardt’s ankle to let it drop to his side, and silenced Linhardt with his mouth, once more. Linhardt whimpered and pulled at Sylvain’s hair, though his hands couldn’t get a good enough grip.

Sylvain’s rhythm increased, and Linhardt could tell by the way his body was shaking, he was just about at his limit. And that would be just fine; Linhardt was pretty much already there. In a few more thrusts, both men came together, their mouths breaking free to cry out in unison.

Linhardt clenched at the feeling of Sylvain filling him up, paired with the spreading warmth of his own seed on his stomach. His nose turned up; _that_ wasn’t a pleasant sensation.

Slowly, Sylvain pulled out with a large sigh, steadied himself above Linhardt. He looked down and smirked. “Well, how did that compare to the first trial?”

Swallowing hard, Linhardt turned his head away, seeing just how badly Sylvain’s arm was shaking. “I didn’t…finish writing those notes, so it’ll take some time to compare.”

“Right.” Sylvain rolled his eyes and got up from the bed, looking around the room. He shrugged and picked up his shirt, turning back to Linhardt. “It won’t be the first time I’ll walk around the monastery topless…”

“What are you…”

Sylvain began to wipe off his own cock with his discarded shirt before moving over to Linhardt, wiping up the milky, sticky mess from his stomach. “I don’t like spooning when there’s a mess.”

“Sp-spooning?”

His hands moved the shirt, trying to get every last bit off Linhardt’s stomach.

Linhardt shuddered and pushed Sylvain away. “That’s enough, please. That fabric is so…”

“Didn’t like that sensation, huh?” Sylvain sighed and plopped onto the bed, pressing his body up against Linhardt’s back and burying his face in his hair.

Closing his eyes, Linhardt’s breathing calmed as Sylvain’s arms wrapped around him. This was…nice. Pleasant, even. He didn’t remember this happening after their last meeting.

“Seriously, I’ve never had a guy want to sleep with me because of my crest. Almost said no, to be honest, but glad I didn’t.” His mouth was up against Linhardt’s ear; his voice, his breath, filling the space. Linhardt bit back his lip to stop any reactions to it.

“For research, Gautier, I told you…”

“Right, that was the caveat,” he said, long emerald strands twirling around his fingers. “I guess that’s what made me say yes. You intrigue me…”

“I suppose I can say the same for you.”

Sylvain laughed, and took a soft bite at the lobe of Linhardt’s ear. “Call on me whenever you need a lab rat. I doubt you’ll be able to write your notes down without getting hard again.”

Linhardt would have rolled his eyes, but closing them came more naturally. “Of course,” he said in a yawn, the warmth of Sylvain’s body helping to lull him into a restful sleep.

There was still so much to jot down, but all that would have to wait…


End file.
